04/16/2009 at 08:40 AM EDT
Despite his recent hospitalization
with stomach pains, Josh Hartnett
assured PEOPLE at Wednesday night's New Yorkers For Children Sixth Annual Spring Dinner, "I'm fine. I just had a little stomach bug."
The Pearl Harbor
star, 30, was staying at the Chateau Marmont in West Hollywood when he began complaining of abdominal pain a little before 2 a.m. on March 30. An ambulance arrived quickly, and he was able to walk into it on his own, his rep, Susan Patricola, said at the time.
On Wednesday, Hartnett said that he thinks the reason why "everyone made such a big deal" about his medical incident was because he was rushed to the emergency room from the West Hollywood celebrity haunt, the Chateau Marmont hotel. "But, that's where I always stay when I'm in L.A.," he says.
Insisting there's "nothing to worry about," Hartnett says of his condition, "It's been reoccurring because I have been spending a lot of time in Third World countries, and I occasionally drank the water when I shouldn't have – and sometimes it catches up with you."
As for what sent him to the emergency room in the first place, he says, "Nothing. I got sick."
"I went to the hospital and it was literally just a 24-hour thing. I was so dehydrated that I needed to be on a couple of IVs, but I'm good," he says.
Seen partying with pals
in Miami and L.A. a week after his hospital release, Hartnett on Wednesday appeared mellow, chatting with tennis star Serena Williams while sipping white wine – and noting, "I'll be around."